1. Field of the Invention
Embodiments generally relate to a seam morphological improvement approach, and, more specifically, to a post ultrasonically-welded seam overcoat treatment for flexible imaging member belts.
2. Background and Summary
Flexible electrostatographic belt imaging members are well known in the art. Typical electrostatographic flexible belt imaging members include, for example, photoreceptors for electrophotographic imaging systems, electroreceptors such as ionographic imaging members for electrographic imaging systems, and intermediate image transfer belts for transferring toner images in electrophotographic and electrographic imaging systems. These belts are usually formed by cutting a rectangular, a square, or a parallelogram shape sheet from a web containing at least one layer of thermoplastic polymeric material, overlapping opposite ends of the sheet, and joining the overlapped ends together to form a welded seam. The seam extends from one edge of the belt to the opposite edge. Generally, these belts comprise at least a supporting substrate layer and at least one imaging layer comprising thermoplastic polymeric matrix material. The imaging layer as employed herein is defined as and refers to any of the dielectric imaging layer of an electroreceptor belt, the transfer layer of an intermediate transfer belt, and the charge transport layer of an electrophotographic belt. Thus, the thermoplastic polymeric matrix material in the imaging layer is generally located in the upper portion of a cross section of an electrostatographic imaging member belt, the substrate layer being in the lower portion of the cross section of the electrostatographic imaging member belt. Although the flexible belts of interest include the mentioned types, for simplicity reasons, the discussion hereinafter will be focus on the electrophotographic imaging member belts.
Between the substrate and imaging layers, such flexible electrophotographic imaging members or multilayered photoreceptors also typically include an electrically conductive layer, an optional hole blocking layer, an adhesive layer, a charge generating layer, and, in some embodiments, an anti-curl backing layer. One type of multilayered photoreceptor comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder to form a layer that is charge generating and charge transporting. A typical layered photoreceptor having separate charge generating (photogenerating) and charge transport layers is described in U.S. Pat. No. 4,265,990, the entire disclosure thereof being incorporated herein by reference. In negatively-charged varieties of such photoreceptors, a charge generating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
Although excellent toner images can be obtained with multilayered belt photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators and printers are developed, fatigue-induced cracking of the charge transport layer at the welded seam area is frequently encountered during photoreceptor belt cycling. Moreover, the onset of seam cracking has also been found to rapidly lead to seam delamination due to fatigue, shortening belt service life. Dynamic fatigue seam cracking can possibly happen in ionographic imaging member belts as well.
As mentioned above, flexible electrostatographic imaging members are typically fabricated from a sheet cut from an imaging member web, generally in a rectangular or parallelogram shape, and a sheet is formed into a belt by joining overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping marginal end regions at the point of joining. Joining can be effected by any suitable means, such as by welding (including ultrasonic), gluing, taping, pressure heat fusing, and the like. Ultrasonic welding is generally the preferred method of joining because it is rapid, clean (no solvents), and produces a thin and narrow seam. In addition, ultrasonic welding is preferred because the mechanical pounding of the welding horn causes generation of heat at the contiguous overlapping end marginal regions of the sheet to maximize melting of one or more layers therein. A typical ultrasonic welding process is carried out by holding down the overlapped ends of a flexible imaging member sheet with vacuum against a flat anvil surface and guiding the flat end of an ultrasonic vibrating horn transversely across the width of the sheet, over and along the length of the overlapped ends, to form a welded seam.
When ultrasonically welded into a belt, the seam of multilayered electrophotographic imaging flexible members can occasionally contain undesirable high protrusions such as peaks, ridges, spikes, and mounds. These seam protrusions present problems during image cycling of the belt machine because they interact with cleaning blades to cause blade wear and tear, which ultimately affects cleaning blade efficiency and service life. Moreover, the protrusion high spots in the seam can also interfere with the operation of subsystems of copiers, printers and duplicators by damaging electrode wires used in development subsystems that position the wires parallel to and closely spaced from the outer imaging surface of belt photoreceptors. These closely spaced wires are employed to facilitate the formation of a toner powder cloud at a development zone adjacent to a toner donor roll and the imaging surface of the belt imaging member. Another frequently observed mechanical failure in the imaging belts during image cycling is that, after being subjected to extended bending and flexing cycles over small diameter belt support rollers, the ultrasonically welded seam of an electrophotographic imaging member can develop cracks that propagate and lead to delamination of the belt. Addtionally, such cracking and delamination can result from lateral forces caused by mechanical rubbing contact against stationary web edge guides of a belt support module during cycling. Seam cracking and delamination is further aggravated when the belt is employed in electrophotographic imaging systems utilizing blade cleaning devices and some operational imaging subsystems. Alteration of materials in the various photoreceptor belt layers such as the conductive layer, hole blocking layer, adhesive layer, charge generating layer, and/or charge transport layer to suppress cracking and delamination problems is not easily accomplished. The alteration of the materials can adversely impact the overall physical, electrical, mechanical, and other properties of the belt such as well as coating layer uniformity, residual voltage, background, dark decay, flexibility, and the like.
As mentioned above, when a flexible imaging member used in an electrophotographic machine is a photoreceptor belt fabricated by ultrasonic welding of overlapped opposite ends of a sheet, the ultrasonic energy transmitted to the overlapped ends melts the thermoplastic sheet components in the overlap region to form a seam. The ultrasonic welded seam of a multilayered photoreceptor belt is relatively brittle and low in strength and toughness. The joining techniques, particularly the welding process, can result in the formation of a splashing that projects out from either side of the seam in the overlap region of the belt. The overlap region and splashings on each side of the overlap region comprise a strip from one edge of the belt to the other that is referred herein as the seam region. The seam region of a typical overlap seamed flexible belt is about 1.6 times thicker than the thickness of the body of the belt. Because of the splashing, a typical flexible imaging member seamed belt has a peak splashing height of about 76 micrometers above the surface of the imaging layer at the junction between the top splashing and the surface of the belt. The junction meeting point is the undesirable site of physical discontinuity which has been found to act as a stress concentration point that facilitates early onset of seam cracking/delamination under the dynamic fatigue-inducing conditions to which imaging members are subjected in normal use.
The photoreceptor belt in an electrophotographic imaging apparatus undergoes bending strain as the belt is cycled over a plurality of support and drive rollers. The excessive thickness of the photoreceptor belt in the seam region due to the presence of the splashing results in a large induced bending strain as the seam travels over each roller. Generally, small diameter support rollers are highly desirable for simple, reliable copy paper stripping systems in electrophotographic imaging apparatus utilizing a photoreceptor belt system operating in a very confined space. Unfortunately, small diameter rollers, e.g., less than about 0.75 inch (19 millimeters) in diameter, raise the threshold of mechanical performance criteria to such a high level that photoreceptor belt seam failure can become unacceptable for multilayered belt photoreceptors. For example, when bending over a 19 millimeter diameter roller, a typical photoreceptor belt seam splashing can develop a 0.96 percent tensile strain due to bending. This is 1.63 times greater than a 0.59 percent induced bending strain that develops within the rest of the photoreceptor belt. Therefore, the 0.96 percent tensile strain in the seam splashing region of the belt represents a 63 percent increase in stress placed upon the seam splashing region of the belt.
Under dynamic fatiguing conditions, the seam provides a focal point for stress concentration and becomes the point of crack initiation which is further developed into seam delamination causing premature mechanical failure in the belt. Thus, the splashing tends to shorten the mechanical life of the seam and service life of the flexible member belts used in copiers, duplicators, and printers.
Although a solution to suppress the seam cracking/delamination problems has been successfully demonstrated, as described in a prior art, by a specific heat treatment process of a flexible electrophotographic imaging member belt with its seam parked directly on top of a 19 mm diameter back support rod for stress-releasing releasing treatment at a temperature slightly above the glass transition temperature (Tg) of the charge transport layer of the imaging member, nevertheless this seam stress release process was also found to produce various undesirable effects such as causing seam area imaging member set and development of belt ripples in the active electrophotographic imaging zones of the belt (e.g., the region beyond about 25.2 millimeters from either side from the midpoint of the seam). Moreover, the heat treatment can induce undesirable circumferential shrinkage of the imaging belt. The set in the seam area of an imaging member mechanically adversely interacts with the cleaning blade and impacts cleaning efficiency. The ripples in the imaging member belt manifest themselves as copy printout defects. Further, the heat induced imaging belt dimensional shrinkage alters the precise dimensional specifications required for the belt. Another key shortcoming associated with the prior art seam stress release heat treatment process is the extensive heat exposure of a large seam area. This extensive heat exposure heats both the seam area of the belt as well as the rod supporting the seam. Since the belt must be cooled to below the glass transition temperature of the thermoplastic material in the belt prior to removal from the support rod to produce the desired degree of seam stress release in each belt, the heat treatment and cooling cycle time is unduly long and leads to very high belt production costs. Additionally, such seam heat treatment stress-release processing does not produce the desired seam surface smoothing and protrusion spot elimination.
Since there is no effective way to prevent the generation of localized high protrusions at the seam, imaging member belts are inspected, right after seam welding belt production process, manually by hand wearing a cotton glove through passing the index finger over the entire seam length and belts found catching the glove by the protrusions are identified as production rejects. Both the time consuming procedure of manual inspection and the number of seamed belts rejected due to the presence of high seam protrusions constitute a substantial financial burden on the production cost of imaging members.
The following references may be of interest: U.S. Pat. No. 5,190,608, issued 2, Mar. 1993 to Darcy et al., discloses a flexible belt having an outwardly facing surface, a welded seam having irregular protrusion on the outwardly facing surface and a thin flexible strip laminated and covering the welded seam and protrusions. This belt can be fabricated by providing a flexible belt having an outwardly facing surface and a welded seam having irregular protrusions on the outwardly facing surface and laminating a thin flexible strip to the welded seam. The belt can be used in an electrostatographic imaging process.
U.S. Pat. No. 5,549,999, issued 27, Aug. 1996 to Swain et al., discloses a process for coating flexible belt seams including providing a flexible belt having an outwardly facing surface and a welded seam, forming a smooth liquid coating comprising a hardenable film forming polymer on the welded seam, the coating being substantially free of fugitive solvent, and hardening the coating to form a smooth solid coating on the seam.
U.S. Pat. No. 5,582,949, issued 10, Dec. 1996 to Bigelow et al., discloses a process for coating flexible belt seams including providing a flexible belt having an outwardly facing surface and a welded seam, forming a smooth liquid coating on the welded seam, the liquid coating comprising a film forming polymer and a fugitive liquid carrier in which the belt surface is substantially insoluble, and removing the fugitive liquid carrier to form a smooth solid coating on the seam.
U.S. Pat. No. 6,328,922 B1, issued 11, Dec. 2001 to Mishra et al., discloses a process for post treatment of an imaging member belt including providing a support member having a smooth flat surface, proving a flexible belt having a welded seam, supporting the inner surface of the seam on the smooth flat surface, contacting the seam with a heated surface, heating the seam region with the heated surface to raise the temperature in the seam region to a temperature of from about 2xc2x0 C. to 20xc2x0 C. about the Tg of the thermoplastic polymer material, and compressing the seam with the heated surface with sufficient compression pressure to smooth out the seam.
U.S. Pat. No. 5,552,005, issued 3, Sep. 1996 to Mammino et al., discloses a flexible imaging sheet and a method of constructing a flexible imaging sheet. The method of constructing a flexible imaging sheet comprises overlapping, joining, and shaping first and second marginal end regions of a sheet to form an overlap region and a non-overlap region joined to one another by a seam in the overlap region with a generally planar surface co-planar with a surface of the non-overlap region. The first and second marginal end regions are secured to one another in the overlap region by the seam, and are substantially co-planar to minimize stress on the flexible imaging sheet. Minimization of stress concentration, resulting from dynamic bending of the flexible imaging sheet during cycling over a roller within an electrophotographic imaging apparatus, is particularly accomplished in the present invention.
U.S. Pat. No. 6,074,504 to Yu et al., issued 13, Jun. 2000, discloses a process for treating a seamed flexible electrostatographic imaging belt including providing an imaging belt having two parallel edges, the belt comprising at least one layer comprising a thermoplastic polymer matrix and a seam extending from one edge of the belt to the other, the seam having an imaginary centerline, providing an elongated support member having at arcuate supporting surface and mass, the arcuate surface having at least a substantially semicircular cross section having a radius of curvature of between about 9.5 millimeters and about 50 millimeters, supporting the seam on the arcuate surface with the region of the belt adjacent each side of the seam conforming to the arcuate supporting surface of the support member, precisely traversing the length of the seam from one edge of the belt to the other with thermal energy radiation having a narrow Gaussian wavelength distribution of between about 10.4 micrometers and about 11.2 micrometers emitted from a carbon dioxide laser, the thermal energy radiation forming a spot straddling the seam during traverse, the spot having a width of between about 3 millimeters and about 25 millimeters measured in a direction perpendicular to the imaginary centerline of the seam, and rapidly quenching the seam by thermal conduction of heat from the seam to the mass of the support member to a temperature below the glass transition temperature of the polymer matrix while the region of the belt adjacent each side of the seam conforms to the arcuate supporting surface of the support member.
While these and other innovative prior art approaches provided improved flexible belt seam morphology, nevertheless it has been found that solution of one problem has also created new undesirable issues. For example, overcoating the seam of a photoreceptor belt with metallic foil can cause electrical seam arcing as the belt cycles beneath a charging device during electrophotographic imaging processes. Additionally, application of liquid overcoating layer over the seam induced charge transport molecule crystallization in the vicinity of the seam overcoat, not to mention that liquid overcoating layer can produce poor adhesion bond strength to the seam after solidification into a dried coat. Thus, there is a continuing need for electrostatographic imaging belts having improved welded seam design that is resistant to seam cracking/delamination, substantially free of seam protrusions, has improved seam region physical continuity, and is substantially free of factors that damage imaging subsystems.
Furthermore, there is an urgent need to provide seamed flexible imaging belts with an improved seam morphology which can withstand greater dynamic fatigue conditions thereby extending belt service life. It is also important, from the imaging member belt production point of view, that effective cutting of unit manufacturing cost of seamed imaging belts can be realized if an innovative post seaming treatment process can be developed and adopted for belt finishing implementation to provide the improvement of morphological seam surface smoothing free of protrusion spots and to effect the elimination of physical discontinuity at the junction meeting point where the top seam splashing making contact with the belt surface.
Embodiments of the instant invention provide such an improved electrostatographic imaging member that substantially overcomes the above-noted deficiencies by providing a morphologically improved seamed electrostatographic imaging member. Embodiments yield an improved electrostatographic imaging member with an ultrasonically welded seam which, after being subjected to post processing, exhibits greater resistance to onset of dynamic fatigue induced seam cracking/delamination problem. After being subjected to post processing according to embodiments, seams exhibit good circumferential dimension tolerance, robust mechanical seam function, and reduced cleaning blade wear. Seams treated according to embodiments are substantially free of seam protrusions, have smoother surface morphological profiles, have little or no seam region physical discontinuity, and have reduced seam area thickness that greatly reduces seam region bending stress when the electrostatographic imaging member flexes over small-diameter belt module support rollers.
These results are achieved according to embodiments by, for example, providing a flexible imaging member seam treatment article preparation method comprising providing a flexible substrate comprising a high-temperature-resistant material, coating a surface of the flexible substrate with a solution including at least one thermoplastic polymer component, and drying the coated surface to form a film of the at least one polymer component on the coated surface. Where the substrate is larger than the size to be applied, the method can additionally comprise cutting the coated flexible substrate into at least one strip sized to cover the seam. Providing a flexible substrate can comprise providing a web of a high-temperature-resistant material, and the method can further comprise forming a roll from the dried, coated flexible substrate, so as to form a tape reel. The flexible substrate can comprise a metallic substrate, a high-glass-transistion-temperature flexible polymeric film, such as a biaxially-oriented PET film. Coating a surface of the flexible substrate can comprise providing a solution including a charge transport compound, which can include dissolving a polycarbonate, such as Makrolon, and the charge transport compound in an organic solvent.
Such results can also be achieved according to embodiments by, for example, providing a belt seam treatment strip preparation method comprising dissolving a thermoplastic polymer into a solvent, applying the dissolved thermoplastic polymer to a surface of a high-temperature-resistant flexible substrate, and eliminating the solvent to form a thermoplastic polymer film on the surface of the substrate. Dissolving a thermoplastic polymer into a solvent can comprise providing an organic solvent, the thermoplastic polymer including at least one of a granular and a powder of a film-forming thermoplastic polymer. Eliminating the solvent can comprise air drying the coated substrate, baking the coated substrate, or any other suitable method. Applying the dissolved thermoplastic polymer can comprise providing a web of high-temperature-resistant flexible substrate onto which the dissolved thermoplastic polymer is applied, which flexible substrate can be a high-glass-transition-temperature flexible polymer substrate, such as a biaxially-oriented PET film, or a metallic film. Dissolving a thermoplastic polymer can comprise providing a charge transport compound, such as N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-1,1xe2x80x2-biphenyl-4,4xe2x80x2-diamine, and can comprise providing a bisphenol-A polycarbonate of Makrolon.
Such results can further be achieved according to embodiments by, for example, providing a flexible imaging belt seam treatment article comprising a high-temperature-resistant flexible substrate supporting a thermoplastic polymer film deposited thereon by dissolution of a film-forming thermoplastic polymer in a carrier solvent, application of a resulting solution to the flexible substrate, and elimination of the carrier solvent. The high-temperature-resistant flexible substrate can comprise a flexible metallic film, a high-glass-transition-temperature polymer sheet, or any other suitable flexible substrate material. The deposited thermoplastic polymer film can comprise, for example, a bisphenol-A polycarbonate, such as Makrolon, and a charge transport compound, such as N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-1,1xe2x80x2-biphenyl-4,4xe2x80x2-diamine.
Although this invention deals with the seam overcoat material formulations, it also relates to apparatus and lamination process for effective flexible electrostatographic imaging member belts seam overcoating application, the following will focus only on seamed flexible electrophotographic imaging member belts to simplify discussion.
A more complete understanding of the process and apparatus of the present invention can be obtained by reference to the accompanying drawings wherein: